Radio station and method of processing user data with radio station

ABSTRACT

A radio station ( 1 ) includes a first part ( 1 A) and at least one second part ( 1 B). The second part ( 1 B) can be arranged so as to be physically separated from the first part ( 1 A) and is connected to the first part ( 1 A) via a transmission line ( 40 ) so as to be able to communicate with the first part. The first part ( 1 A) performs dynamic scheduling to allocate a plurality of radio resources to a plurality of mobile stations or user data. The second part ( 1 B) performs signal processing including channel coding for transmitting downlink user data to an air interface and channel decoding for restoring uplink user data from a signal received from the air interface.

TECHNICAL FIELD

The present invention relates to a configuration of a radio station (e.g., a radio base station, a relay station) used in a radio communication network.

BACKGROUND ART

A structure of a radio base station including a radio equipment controller (REC) and a radio equipment (RE), which are separated from each other, is disclosed in Patent Literature 1 and Non-Patent Literature 1. The REC and the RE are at least functionally separated from each other. The REC and the RE are connected to each other through an internal interface (communication interface) of the radio base station. The REC and the RE may be arranged so as to be physically spaced apart from each other. In a typical layout, the REC is arranged in a main building of a telecom carrier and the RE is arranged at a remote location near an antenna.

The REC is connected to an upper network (e.g., a core network of a telecom carrier). The REC plays a role in controlling and monitoring the entire radio base station and performing digital baseband signal processing. In this case, the digital baseband signal processing includes layer-2 signal processing and layer-1 (physical layer) signal processing. The layer-2 signal processing includes at least one of (i) data compression/de-compression, (ii) data encryption, (iii) addition/removal of a layer-2 header, (iv) data segmentation/concatenation, and (v) composition/decomposition of a transfer format by data multiplexing/de-multiplexing. In the case of E-UTRA, as a specific example, the layer-2 signal processing includes processing of Radio Link Control (RLC) and Media Access Control (MAC). The physical layer signal processing includes channel coding/decoding, modulation/demodulation, spreading/de-spreading, resource mapping, and generation of OFDM symbol data (baseband OFDM signal) by Inverse Fast Fourier Transform (IFFT).

The RE plays a role in performing analog radio frequency (RF) signal processing, and provides an air interface to a mobile station. The analog radio frequency (RF) signal processing includes D/A conversion, A/D conversion, frequency up-conversion, frequency down-conversion, and amplification. The RE is also referred to as a remote radio head (RRH).

For example, in the case of a radio access network of a universal mobile telecommunications system (UMTS), the REC provides a connection to a radio network controller (RNC) using an Iub interface for sending and receiving user data (user plane data) and control data (control plane data). On the other hand, the RE provides a mobile station with an air interface called a Uu interface.

In the case of Evolved Universal Terrestrial Radio Access (E-UTRA), the REC provides a connection to an evolved packet core (EPC) using an S1 interface for sending and receiving user data and control data. On the other hand, the RE provides a mobile station with an air interface called an LTE-Uu interface.

As described above, the separated structure of the radio base station disclosed in Patent Literature 1 and Non-Patent Literature 1 is characterized in that a part that performs analog RF signal processing is separated as the RE. This separated structure makes it possible to flexibly and effectively deal with an increase and a change in the functions implemented in the radio base station. In addition, this separated structure makes it possible to easily deal with independent advancement of an analog RF technique and a digital baseband technique by separating the two techniques.

CITATION LIST Patent Literature

-   Patent literature 1: International Patent Publication No. WO     2004/095861

Non-Patent Literature

-   Non-Patent literature 1: Common Public Radio Interface (CPRI)     Specification V4.2 (2010-09-29), [online], September, 2010, Ericsson     AB, Huawei Technologies Co. Ltd, NEC Corporation, Alcatel Lucent and     Nokia Siemens Networks GmbH & Co. KG, [retrieved on Oct. 20, 2011],     Internet <URL:http://www.cpri.info/spec.html>

SUMMARY OF INVENTION Technical Problem

It is predicted that as the traffic (user data) to be processed by the radio base station increases, the traffic between the REC and the RE also increases. However, in the separated structure disclosed in Patent Literature 1 and Non-Patent Literature 1, the REC performs digital signal processing (channel coding, modulation, spreading, generation of an OFDM signal, etc.) on the physical layer. The channel coding, spreading, and the like increase the redundancy of transmitted data. Accordingly, the data amount of a transmitted data stream obtained by performing the digital signal processing on the physical layer is generally larger than that of a data stream before performing the digital signal processing. For this reason, in the separated structure disclosed in Patent Literature 1 and Non-Patent Literature 1, traffic congestion in a communication line between the REC and the RE may occur due to an increase in traffic in the future. On the other hand, when all the baseband signal processing performed at the REC is simply moved to the RE, it is difficult to perform radio resource management cooperatively between the REC and a plurality of REs. The radio resource management without cooperation may cause inefficiency in use of radio resources and degradation in system performance.

Therefore, it is an object of the present invention to provide a radio station having a separated structure and a method of processing user data capable of easily dealing with an increase in traffic (user data) and performing cooperative control between cells.

Solution to Problem

A first aspect of the present invention includes a radio station that is used in a radio communication network and is capable of transmitting and receiving user data including downlink user data and uplink user data to and from a plurality of mobile stations via an air interface. The radio station includes a first part and at least one second part that can be arranged so as to be physically separated from the first part and is connected to the first part via a transmission line so as to be able to communicate with the first part. The first part is configured to perform dynamic scheduling to allocate a plurality of radio resources to the plurality of mobile stations or the user data. The second part is configured to perform signal processing including channel coding for transmitting the downlink user data to the air interface and channel decoding for restoring the uplink user data from a signal received from the air interface.

A second aspect of the present invention includes a method of processing user data performed by a radio station. The radio station is used in a radio communication network and is configured to transmit and receive user data including downlink user data and uplink user data to and from a plurality of mobile stations via an air interface. The radio station includes a first part and at least one second part that can be arranged so as to be physically separated from the first part and is connected to the first part via a transmission line so as to be able to communicate with the first part. The processing method according to this aspect includes:

(A) performing, in the first part, dynamic scheduling to allocate a plurality of radio resources to the plurality of mobile stations or the user data; and

(B) performing, in the second part, signal processing including channel coding for transmitting the downlink user data to the air interface and channel decoding for restoring the uplink user data from a signal received from the air interface.

Advantageous Effects of Invention

According to the above-mentioned aspects of the present invention, it is possible to provide a radio station having a separated structure and a method of processing user data capable of easily dealing with an increase in traffic (user data) and performing cooperative control between cells.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration example of a radio base station according to a first embodiment of the invention;

FIG. 2 is a diagram showing a functional layout of the radio base station according to the first embodiment of the invention;

FIG. 3 is a block diagram showing a configuration example of a radio base station according to a second embodiment of the invention;

FIG. 4 is a diagram showing a protocol structure and a functional layout of the radio base station according to the second embodiment of the invention;

FIG. 5 is a block diagram showing a configuration example of a radio base station according to a third embodiment of the invention;

FIG. 6 is a diagram showing a functional layout of the radio base station according to the third embodiment of the invention;

FIG. 7 is a block diagram showing a configuration example of a radio base station according to a fourth embodiment of the invention;

FIG. 8 is a block diagram showing a configuration example of a radio base station according to a fifth embodiment of the invention;

FIG. 9 is a block diagram showing a configuration example of a radio base station according to a sixth embodiment of the invention;

FIG. 10 is a sequence diagram showing operation examples of a primary scheduler and a secondary scheduler according to the sixth embodiment of the invention;

FIG. 11 is a sequence diagram showing operation examples of the primary scheduler and the secondary scheduler according to the sixth embodiment of the invention;

FIG. 12 is a block diagram showing a configuration example of a radio base station according to a seventh embodiment of the invention; and

FIG. 13 is a diagram showing a functional layout of the radio base station according to the seventh embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

Specific embodiments of the present invention will be described in detail below with reference to the drawings. The same or corresponding components are denoted by the same reference numerals throughout the drawings, and a repeated description thereof is omitted as needed to clarify the explanation. In the following description, E-UTRA/LTE (Long Term Evolution) radio base stations will be mainly described. However, such a specific radio communication system is described not to limit the scope of the present invention, but to facilitate understanding of the present invention. In other words, those skilled in the art can apply the principle and idea grasped from the embodiments described in detail below to various radio communication systems.

First Embodiment

FIG. 1 is a block diagram showing a configuration of a radio base station 1 according to this embodiment. The radio base station 1 is used in a radio communication network and is capable of transmitting and receiving user data including downlink user data and uplink user data to and from a plurality of mobile stations via an air interface. The radio base station 1 includes a first part, i.e., a radio equipment controller (REC) 1A, and at least one second part, i.e., a radio equipment (RE) 1B. The RE 1B can be arranged so as to be physically separated from the REC 1A via a transmission line 40, and is connected to the REC 1A so as to be able to communicate with the REC 1A via the transmission line 40. The transmission line 40 may be an electrical transmission line or an optical transmission line. Alternatively, the transmission line 40 may be a point-to-point type radio transmission line (e.g., a microwave radio transmission line). The transmission line 40 may include a plurality of physical transmission lines for bidirectional transmission. As shown in FIG. 1, a plurality of REs 1B may be connected to the REC 1A.

Internal interfaces 30 and 31, which are arranged in the REC 1A and the RE 1B, respectively, have layer-2 and layer-1 functions for bidirectional communication via the transmission line 40. The internal interface 30 may be an electrical interface, an optical interface, or a radio interface. For example, an existing transceiver, such as 1000BASE-CX, 1000BASE-SX, 1000BASE-LX, 10GBASE-LX4, or a fibre channel, may be used as the internal interface 30.

The REC 1A includes a scheduler 20. The scheduler 20 performs dynamic scheduling for the downlink and uplink. In other words, the scheduler 20 dynamically allocates a plurality of downlink and uplink radio resources to a plurality of mobile stations or user data. The radio resources are distinguished by time, frequency, or spreading code, or a combination thereof. For example, in the case of E-UTRA, dynamic scheduling is performed assuming that each radio resource is a resource block and two resource blocks within one sub-frame (1 msec) are defined as a minimum unit. One resource block includes 12 subcarriers in a frequency domain, and includes seven OFDM symbols in a time domain.

The dynamic scheduling for the downlink is achieved by selecting data to be allocated to each radio resource from a buffer 21, by using a scheduling technique such as Proportional Fairness (PF), max-C/I (carrier/interference), or round robin. The buffer 21 temporarily stores the downlink user data which has arrived from an upper network. The buffer 21 is prepared, for example, for each mobile station, for each bearer, for each QoS class, or for each mobile station and each QoS class. The unit in which the buffer 21 is prepared is determined as appropriate depending on the layout of the buffer, requirements for scheduling (e.g., the presence or absence of a QoS class, the necessity to secure a transmission rate), or the like. In addition, there is a degree of freedom in the layout of the buffer 21, and thus the layout of the buffer 21 is not limited to the layout shown in FIG. 1.

The dynamic scheduling for the uplink is performed based on, for example, the reception of a resource allocation request from a mobile station, or a monitoring result of a data buffer arranged in the mobile station. The dynamic scheduling for the uplink is achieved by determining mobile stations to be allocated to radio resources, by using a scheduling technique such as PF, max-C/I, or round robin.

Further, in the case of E-UTRA, as a specific example, the dynamic scheduling performed by the scheduler 20 includes selection of a payload in a radio link control (RLC) sublayer, control of re-transmission in a MAC sublayer, and designation of a coding rate, a modulation scheme and a radio resource in a physical layer. Control information relating to the dynamic scheduling are sent to a layer-2 unit 11 and a BB-PHY unit 12 via the transmission line 40 by signaling as indicated by dashed lines in FIG. 1.

On the other hand, the RE 1B includes the BB-PHY unit 12 and an RF-PHY unit 13. The BB-PHY unit 12 performs digital baseband signal processing on the physical layer. More specifically, the signal processing performed by the BB-PHY unit 12 includes channel coding and modulation for transmitting the downlink user data to the air interface. The signal processing performed by the BB-PHY unit 12 also includes demodulation and channel decoding for restoring the uplink user data from the signal received from the air interface. The channel coding and decoding by the BB-PHY unit 12 includes, for example, block coding or convolutional coding, or a combination thereof. The channel coding and decoding by the BB-PHY unit 12 are performed by using, for example, a coding algorithm such as turbo code, Viterbi code, or Reed-Solomon code. Depending on the communication system, the signal processing performed by the BB-PHY unit 12 may include, for example, spreading/de-spreading, resource mapping, and generation of an OFDM signal involving Inverse Fast Fourier Transform (IFFT).

The RF-PHY unit 13 is connected to an antenna 14, and performs analog RF signal processing on the physical layer. The signal processing performed by the RF-PHY unit 13 includes D/A conversion, A/D conversion, frequency up-conversion, frequency down-conversion, and amplification.

As described above, in the radio base station 1 according to this embodiment, the scheduler 20 is arranged in the REC 1A, and the BB-PHY unit 12 is arranged in the RE 1B. In other words, in the radio base station 1, the RE 1B performs digital signal processing, on the physical layer, including at least channel coding and decoding. Thus, since the data stream that contains the user data and is transmitted via the transmission line 40 does not include redundant data generated as a result of channel coding (e.g., block coding, convolutional coding, or turbo coding), the data amount to be transmitted between the REC 1A and the RE 1B can be suppressed. Therefore, the radio base station 1 has an advantage of being able to easily deal with an increase in traffic, as compared with the case of performing channel coding and decoding in the REC 1A.

Further, the radio base station 1 employs an architecture in which the scheduler 20 is arranged in the REC 1A, instead of arranging all the baseband signal processing in the RE 1B. This allows the radio base station 1 to perform cooperative scheduling at the REC 1A in consideration of radio resources required for each of the plurality of REs 1B. Accordingly, the radio base station 1 can effectively use radio resources by performing cooperative control between cells, as compared with the case of performing scheduling at a distributed manner among the respective REs 1B.

The layout of a bearer termination unit 10, the layer-2 unit 11, and sub-units included therein can be modified in various manners. In other words, the bearer termination function and the layer-2 processing function can be appropriately distributed between the REC 1A and the RE 1B. Various additional effects can be obtained by adjusting the layout of these functional units. Various aspects of the layout of these functional units will be described later in this embodiment and other embodiments.

A layout example of the functional units shown in FIG. 1 will be described in detail below. In the example of FIG. 1, the bearer termination unit 10 is arranged in the REC 1A. The bearer termination unit 10 terminates a bearer established between the radio base station 1 and an upper network (e.g., RNC of UMTS, EPC of E-UTRA) so as to transfer user data. In general, a bearer (e.g., an S1 bearer of E-UTRA) for transferring user data is encrypted with a tunneling protocol (e.g., IPsec). A bearer is established for each data flow (e.g., a Packet Data Network (PDN) connection of E-UTRA) between each mobile station and an external network. Accordingly, the bearer termination unit 10 terminates a plurality of encrypted bearers, receives the downlink user data pertaining to the plurality of mobile stations from the upper network, and sends the uplink user data pertaining to the plurality of mobile stations to the upper network.

In the example of FIG. 1, the layer-2 unit 11 is arranged in the RE 1B. The layer-2 unit 11 performs layer-2 signal processing except for dynamic scheduling, utilizing the bearer termination unit 10 as an upper protocol layer and the BB-PHY unit 12 as a lower protocol layer. The layer-2 signal processing includes at least one of (i) data compression/de-compression, (ii) data encryption, (iii) addition/removal of a layer-2 header, data segmentation/concatenation, and (v) composition/decomposition of a transfer format by data multiplexing/de-multiplexing.

In the case of E-UTRA, as a specific example, the layer-2 signal processing includes processing of the RLC sublayer and the MAC sublayer. The RLC sublayer uses the bearer termination unit 10 as an upper protocol layer. In the MAC sublayer, the RLC sublayer is defined as an upper protocol layer, and the BB-PHY unit 12 is defined as a lower protocol layer. The E-UTRA further includes a PDCP sublayer as an upper sublayer of the RLC sublayer. However, processing (e.g., IP header compression, encryption) in the PDCP sublayer is not essential and may be omitted.

In the case of E-UTRA, the PDCP sublayer plays a role in performing processing for reducing the data amount to be transmitted in a manner suitable for the transmission and reception via the air interface. Specifically, the PDCP sublayer performs IP header compression for the downlink user data, and IP header de-compression for the uplink user data. The PDCP sublayer also performs encryption of the user data, and duplication and transfer of the user data so as to reduce a delay in handover.

The RLC sublayer of the E-UTRA performs segmentation and concatenation and re-transmission control for radio bearer data (PDCP Protocol Data Unit (PDUs)) supplied from the PDCP sublayer. The RLC sublayer provides, to the PDCP sublayer, a data transfer service using a radio bearer. The RLC sublayer is connected to the MAC sublayer through a logical channel (RLC PDUs).

The MAC sublayer of the E-UTRA performs multiplexing of the logical channels (RLC PDUs), and hybrid-ARQ (automatic repeat request) re-transmission. The MAC sublayer generates a transport channel by multiplexing the logical channels (RLC PDUs). The transmission format (data block size) of the transport channel depends on an instantaneous data rate. The MAC sublayer is connected to the physical layer (BB-PHY unit 12) through the transport channel (MAC PDUs).

As described above, the layout of the bearer termination unit 10 and the layer-2 unit 12 shown in FIG. 1 is illustrated by way of example, and is not limited to this layout. For example, the bearer termination unit 10 may be arranged in the RE 1B. The whole or a part (e.g., PDCP sublayer) of the layer-2 unit 12 may be arranged in the REC 1A. Such modified examples will be described in the second and subsequent embodiments.

In the example of FIG. 1, the buffer 21 is arranged between the bearer termination unit 10 and the layer-2 unit 11. Accordingly, the buffer 21 stores the user data (e.g., IP packets) itself before performing data compression, encryption, segmentation and multiplexing in the layer-2 processing. However, such a layout of the buffer 21 is illustrated by way of example only. The buffer 21 may be arranged so as to store the user data stream obtained by performing the data compression and encryption in the layer-2. In the case of E-UTRA, the user data stream obtained by performing the data compression and encryption in the layer-2 corresponds to the PDCP Protocol Data Units (PDUs), which are a data stream obtained after the PDCP sublayer is processed (i.e., radio bearer data). Alternatively, the buffer 21 may be arranged so as to store the user data stream obtained by performing segmentation/concatenation and addition of a layer-2 header in the layer-2. In the case of E-UTRA, the user data stream obtained by performing the segmentation/concatenation and addition of a layer-2 header corresponds to the RLC PDUs, which are a data stream obtained after the Radio-Link Control (RLC) sublayer is processed (i.e., a logical channel).

As a modification of the layout of the buffer 21 described above, the buffer 21 may be arranged in the RE 1B. For example, the buffer 21 may be arranged between the layer-2 unit 11 and the internal interface 31 of the RE 1B shown in FIG. 1. Alternatively, the buffer 21 may be arranged between a PDCP unit (not shown) and an RLC unit (not shown) in the layer-2 unit 11 so as to store the data stream (i.e., PDCP PDUs) including user data.

The scheduler 20, however, needs to recognize the storage status of the buffer 21 during the dynamic scheduling for the downlink. Accordingly, both the buffer 21 and the scheduler 20 are arranged in the REC 1A, thereby facilitating the dynamic scheduling. Moreover, the amount of control data to be transferred between the internal interfaces 30 and 31 can be reduced. The REC 1A (the internal interface 30) may selectively transmit data selected by the scheduler 20 from the downlink user data or from the data stream including the downlink user data stored in the buffer 21.

FIG. 2 shows the details of the functional layout in the radio base station 1 regarding the downlink transmission of user data in the E-UTRA. The functional layout shown in FIG. 2 corresponds to a specific example of the functional layout shown in FIG. 1. For example, the layer-2 unit 11 includes three sub-units, i.e., a PDCP unit 110, an RLC unit 111, and a MAC unit 112. The PDCP unit 110 performs processing on the PDCP sublayer. The RLC unit 111 performs processing on the RLC sublayer. The MAC unit 112 performs processing on the MAC sublayer. The BB-PHY unit 12 includes a coding unit 120, a modulation unit 121, a resource mapping unit 122, and an IFFT unit 123. The RF-PHY unit 13 includes an up-converter 130 and an amplifier 131.

Second Embodiment

FIG. 3 is a block diagram showing a configuration example of a radio base station 2 according to this embodiment. The radio base station 2 includes a first part, i.e., a radio equipment controller (REC) 2A, and at least one second part, i.e., a radio equipment (RE) 2B. The radio base station 2 differs from the above-described radio base station 1 in that the bearer termination unit 10 is arranged not in the REC 2A but in the RE 2B. Specifically, in the radio base station 2, the dynamic scheduling by the scheduler 20 is performed at the REC 2A. Further, in the radio base station 2, the termination of a bearer (e.g., an S1 bearer), layer-2 signal processing, and digital baseband signal processing on the physical layer are performed at the RE 2B.

In the radio base station 2, the scheduler 20 is arranged in the REC 2A and the BB-PHY unit 12 is arranged in the RE 2B, as in the radio base station 1. Accordingly, the radio base station 2 can suppress the data amount to be transmitted via the transmission line 40 and perform cooperative scheduling at the REC 2A, as in the radio base station 1.

Further, in the radio base station 2, the encrypted bearer data (e.g., S1 bearer data) is transferred from the REC 2A to the RE 2B via the transmission line 40. This allows the radio base station 2 to enhance security between the REC 2A and the RE 2B. As described above, the RE 2B is expected to be arranged at a remote location that is easily accessed by a third party. Transmission of the encrypted bearer data, instead of the user data, makes it possible to protect the user data against unauthorized access.

FIG. 4 shows the details of the functional layout in the radio base station 2 regarding the downlink transmission of user data in the E-UTRA. As described above, in this embodiment, the bearer termination unit 10 is arranged in the RE 2B. Accordingly, the encrypted bearer data (e.g., S1 bearer data) is transferred from the REC 2A to the RE 2B.

In the example shown in FIGS. 3 and 4, the buffer 21 is arranged in the REC 2A. Accordingly, the buffer 21 shown in FIGS. 3 and 4 may store the encrypted bearer data for each mobile station, for each bearer, for each QoS class, or for each mobile station and each QoS class. However, as described in detail in the first embodiment, the layout of the buffer 21 can be changed as needed. For example, the buffer 21 may be arranged in the RE 2B.

Third Embodiment

FIG. 5 is a block diagram showing a configuration example of a radio base station 3 according to this embodiment. The radio base station 3 includes a first part, i.e., a radio equipment controller (REC) 3A, and at least one second part, i.e., a radio equipment (RE) 3B. Though only one RE 3B is illustrated in FIG. 5, a plurality of REs 3B may be connected to the REC 3A as shown in FIG. 1. The radio base station 3 differs from the above-described radio base station 1 in that the PDCP unit 110 is arranged not in the RE 3B but in the REC 3A. The PDCP unit 110 is a sub-unit included in the layer-2 unit 11. Specifically, the REC 3A performs the dynamic scheduling by the scheduler 20, termination of a bearer (e.g., an S1 bearer), and processing (e.g., IP header compression, encryption) of the PDCP sublayer. On the other hand, the RE 3B performs processing on the RLC sublayer and the MAC sublayer and digital baseband signal processing on the physical layer.

In the radio base station 3, the scheduler 20 is arranged in the REC 3A and the BB-PHY unit 12 is arranged in the RE 3B, as in the radio base station 1. Accordingly, the radio base station 3 can suppress the data amount to be transmitted via the transmission line 40 and perform cooperative scheduling at the REC 3A, as in the radio base station 1.

Furthermore, in the radio base station 3, the REC 3A performs the bearer termination. Thus, the header added to the encrypted bearer data (e.g., S1 bearer data) can be reduced. This leads to a reduction in the data amount to be transferred between the REC 3A and the RE 3B, as compared with the case of transmitting the bearer data to the RE 3B.

In the configuration example of FIG. 5, processing of the PDCP sublayer is also performed at the REC 3A. In the PDCP sublayer, header compression for the user data is performed so as to reduce the data amount to be transmitted via the air interface. Accordingly, the data amount to be transferred between the REC 3A and the RE 3B can be further reduced.

FIG. 6 shows the details of the functional layout in the radio base station 3 regarding the downlink transmission of user data in the E-UTRA. As described above, in this embodiment, the bearer termination unit 10 and the PDCP unit 110 are arranged in the REC 3A. Accordingly, the data stream (PDCP PDUs) on which header compression is performed are transferred from the REC 3A to the RE 3B.

In the example shown in FIGS. 5 and 6, the buffer 21 is arranged in the REC 3A. Accordingly, the buffer 21 shown in FIGS. 5 and 6 may store the PDCP PDUs for each mobile station, for each bearer, for each QoS class, or for each mobile station and each QoS class. However, as described in detail in the first embodiment, the layout of the buffer 21 can be changed as needed. For example, the buffer 21 may be arranged in the RE 3B. Alternatively, the buffer 21 may be arranged between the bearer termination unit 10 and the PDCP unit 110.

Fourth Embodiment

FIG. 7 is a block diagram showing a configuration of a radio base station 4 according to this embodiment. The radio base station 4 includes a first part, i.e., a radio equipment controller (REC) 4A, and at least one second part, i.e., a radio equipment (RE) 4B. The radio base station 4 differs from the above-described radio base station 1 in that bearer termination units 10A and 10B are arranged in the REC 4A and the RE 4B, respectively, and termination points of a plurality of bearers (e.g., an S1 bearer) between an upper network and the radio base station 4 are selectable between the REC 4A and the RE 4B. A bearer termination point may be selected for each bearer, or for each cell. Alternatively, bearer termination points may be collectively selected for all bearers terminated in the radio base station 4.

An example of collectively selecting termination points of all bearers terminated in the radio base station 4 will be described below. For example, bearer termination points may be selected based on a security level of the transmission line 40 between the REC 4A and the RE 4B. More specifically, when the security level of the transmission line 40 is relatively high, the bearers may be terminated in the REC 4A, and when the security level of the transmission line 40 is relatively low, the bearers may be terminated in the RE 4B. The case where the security level of the transmission line 40 is relatively high is, for example, when the transmission line 40 is a dedicated line of a telecom carrier, or when the transmission line 40 is laid on the premises managed by the telecom carrier. The case where the security level of the transmission line 40 is relatively low is, for example, when the transmission line 40 is a general public line, or when the transmission line 40 is laid in a place that is not under full control.

Bearer termination points may be selected at the time of setting up the radio base station 4. Alternatively, bearer termination points may be selected according to switching of the transmission line 40, for example, switching between a main transmission line and a backup transmission line. Specifically, a controller (not shown) of the radio base station 4 may switch the termination points according to the respective security levels of the main transmission line and the backup transmission line when the main transmission line and the backup transmission line have different security levels. Such switching of bearer termination points may be performed according to an instruction from an external device, such as a resource control device or an OAM (Operation Administration and Maintenance) system, which are arranged outside (e.g., an upper network) of the radio base station 4.

Next, an example of individually selecting a termination point for each bearer will be described. For example, a bearer termination point may be selected based on a security level or a QoS class required for each bearer. Specifically, bearers requiring a high security level and bearers to which a high QoS class is set may be terminated in the RE 4B. The other bearers may be terminated in the REC 4A.

In the radio base station 4, the scheduler 20 is arranged in the REC 4A and the BB-PHY unit 12 is arranged in the RE 4B, as in the radio base station 1. Accordingly, the radio base station 4 can suppress the data amount to be transmitted via the transmission line 40 and perform cooperative scheduling at the REC 4A, as in the radio base station 1.

Furthermore, according to this embodiment, the bearer termination in the REC 4A, which contributes to a reduction in the data amount to be transmitted via the transmission line 40, and the bearer termination in the RE 4B, which contributes to an improvement of the security level of the transmission line 40, can be flexibly used depending on the situation.

In the example of FIG. 7, the buffer 21 is arranged in the REC 4A. However, as described in detail in the first embodiment, the layout of the buffer 21 can be changed as needed. For example, the buffer 21 may be arranged in the RE 4B.

Fifth Embodiment

FIG. 8 is a block diagram showing a configuration example of a radio base station 5 according to this embodiment. The configuration example shown in FIG. 8 is a modification of the radio base station 3 shown in FIG. 5. The radio base station 5 includes a first part, i.e., a radio equipment controller (REC) 5A, and at least one second part, i.e., a radio equipment (RE) 5B. Though only one RE 5B is illustrated in FIG. 8, a plurality of REs 5B may be connected to the REC 5A as shown in FIG. 1. The radio base station 5 differs from the radio base station 3 shown in FIG. 5 in that the REC 5A includes a handover (HO) control unit 50. The configuration and functional layout of the RE 5B are the same as those of the RE 3B shown in FIGS. 5 and 6.

When a mobile station communicating over an air interface performs handover to another base station (target base station), the HO control unit 50 transfers the downlink user data pertaining to the mobile station held in the buffer 21, or the data stream including the downlink user data, to the target base station. The transfer of the user data to the target base station is performed in the same manner as in a typical handover procedure. Specifically, the user data may be transferred to the target base station by using an interface (e.g., an X2 interface) available between base stations, or may be transferred via an upper network.

In the radio base station 5, the scheduler 20 is arranged in the REC 5A and the BB-PHY unit 12 is arranged in the RE 5B, as in the radio base station 1. Accordingly, the radio base station 5 can suppress the data amount to be transmitted via the transmission line 40 and perform cooperative scheduling at the REC 5A, as in the radio base station 1.

Further, in the configuration example shown in FIG. 8, the REC 5A buffers the PDCP PDUs, thereby facilitating the data transfer to the target base station during the handover. In other words, there is no need to transfer the data from the RE 5B to the REC 5A during the handover. When a mobile station moves between REs 5B connected to the REC 5A, it is only necessary for the REC 5A to change the transmission destination of the buffered PDCP PDUs to the RE 5B as the handover target. This makes it possible to easily provide continuous services by following the movement of a mobile station.

Although the RLC unit 111 and the MAC unit 1112 are arranged in the RE 5B in the configuration example shown in FIG. 8, these units may be arranged in the REC 5A.

Sixth Embodiment

FIG. 9 is a block diagram showing a configuration example of a radio base station 6 according to this embodiment. The configuration example shown in FIG. 9 is a modification of the radio base station 3 shown in FIG. 5. The radio base station 6 includes a first part, i.e., a radio equipment controller (REC) 6A, and at least one second part, i.e., a radio equipment (RE) 6B. Though only one RE 6B is illustrated in

FIG. 9, a plurality of REs 6B may be connected to the REC 6A as shown in FIG. 1. The radio base station 6 differs from the radio base station 3 shown in FIG. 5 in that the REC 6A includes a primary scheduler 20A and the RE 6B includes a secondary scheduler 20B.

In the radio base station 6, the primary scheduler 20A is arranged in the REC 6A and the BB-PHY unit 12 is arranged in the RE 6B. Accordingly, the radio base station 6 can suppress the data amount to be transmitted via the transmission line 40 and perform cooperative scheduling at the REC 6A, as in the radio base station 1.

Further, in this embodiment, the secondary scheduler 20B performs a part of the processing related to dynamic scheduling. The secondary scheduler 20B operates in a cooperative manner with the primary scheduler 20A for the dynamic scheduling. A specific example of dividing the functions between the primary scheduler 20A and the secondary scheduler 20B will be described below.

In a first example, the secondary scheduler 20B calculates a parameter used for dynamic scheduling based on the radio communication quality of the air interface, and sends the parameter to the primary scheduler 20A. The main scheduling techniques, such as

PF scheduling and Max-C/I scheduling, use the radio communication quality of the air interface. For example, PF scheduling uses, as a parameter, a ratio between an instantaneous predicted radio communication quality and a previous average radio communication quality of a mobile station so as to secure the fairness of transmission opportunities among mobile stations. This parameter is called a PF metric. Examples of the radio communication quality used for calculation of the PF metric include a data rate and a signal-to-interference ratio (SINR). The PF metric is calculated as, for example, a ratio between an instantaneous SINR and an average SINR (i.e., instantaneous SINR/average SINR).

The secondary scheduler 20B calculates a parameter, such as the PF metric, using the radio communication quality, thereby reducing the processing load of the primary scheduler 20A. Further, the data amount to be transmitted from the RE 6B to the REC 6A via the transmission line 40 can be reduced. In the case of calculating a parameter (e.g., PF metric) in the REC 6A, it is necessary to send the measurement results of the current and previous radio communication qualities to the REC 6A from the RE 6B. However, when the secondary scheduler 20B calculates a parameter, only the calculated parameter may be sent instead of the measurement results of the current and previous radio communication qualities.

FIG. 10 is a sequence diagram showing operations of the primary scheduler 20A and the secondary scheduler 20B when the secondary scheduler 20B calculates the PF metric. In step S11, a mobile station (UE) sends quality information. This quality information indicates the downlink radio communication quality measured by the mobile station. In step S12, the secondary scheduler 20B calculates the PF metric by using the quality information received from the mobile station. In step S13, the secondary scheduler 20B sends the PF metric to the primary scheduler 20A. In step S14, the primary scheduler 20A executes dynamic scheduling by using the PF metric received from the secondary scheduler 20B, and determines mobile stations or user data to be allocated to downlink radio resources.

Next, a second example of dividing the functions between the primary scheduler 20A and the secondary scheduler 20B will be described. In the second example, the secondary scheduler 20B executes scheduling for H-ARQ re-transmission or scheduling for re-transmission of the RLC sublayer. Specifically, the secondary scheduler 20B buffers the downlink transmitted data, and when the mobile station requests a re-transmission, the secondary scheduler 20B performs re-transmission based on a re-transmission instruction from the primary scheduler 20A. For example, the secondary scheduler 20B may allocate, for the re-transmission, the same radio resource as that used for the transmission immediately before. This contributes to a reduction in the processing load of the primary scheduler 20A. Further, since there is no need to transfer the re-transmitted data from the REC 6A to the RE 6B, the data amount to be transmitted via the transmission line 40 can be reduced.

FIG. 11 is a sequence diagram showing operations of the primary scheduler 20A and the secondary scheduler 20B when the secondary scheduler 20B controls re-transmission. In step S21, the secondary scheduler 20B buffers the downlink transmitted data. In step S22, the mobile station sends a re-transmission request (e.g., NACK), and the primary scheduler 20A receives this request. In step S23, the primary scheduler 20A instructs the secondary scheduler 20B to perform re-transmission. In step S24, the secondary scheduler 20B performs re-transmission according to the instruction from the primary scheduler 20A.

As is apparent from the descriptions of the first to fifth embodiments, the functional layout in the configuration example shown in FIG. 9 is illustrated by way of example only. For example, the PDCP unit 110 may be arranged in the RE 6B. The bearer termination unit 10 may also be arranged in the RE 6B. As described in the fourth embodiment, the bearer termination unit (10A and 10B) may be arranged in each of the REC 6A and the RE 6B so as to be able to select a bearer termination point. The buffer 21 may also be arranged in the RE 6B.

Seventh Embodiment

FIG. 12 is a block diagram showing a configuration example of a radio base station 7 according to this embodiment. The radio base station 7 includes a first part, i.e., a radio equipment controller (REC) 7A, and at least one second part, i.e., a radio equipment (RE) 7B. The radio base station 7 differs from the above-described radio base station 1 in that the layer-2 unit 11 is arranged in the REC 7A. In the configuration example of FIG. 12, the PDCP unit 110, the RLC unit 111, and the MAC unit 112 correspond to the layer-2 unit 11.

In the radio base station 7, the scheduler 20 is arranged in the REC 7A and the BB-PHY unit 12 is arranged in the RE 7B, as in the radio base station 1. Accordingly, the radio base station 7 can suppress the data amount to be transmitted via the transmission line 40 and perform cooperative scheduling at the REC 7A, as in the radio base station 1.

Further, since the layer-2 unit 11 is arranged in the REC 7A in the radio base station 7, the digital signal processing can be performed in a distributed manner between the REC 7A and the RE 7B. Furthermore, according to this embodiment, the layer-2 unit 11, which is arranged in the REC 7A, can be shared for processing of the user data pertaining to a plurality of REs 7B. Therefore, the layer-2 unit 11 can be effectively used.

FIG. 13 shows the details of the functional layout in the radio base station 7 regarding the downlink transmission of user data in the E-UTRA. As described above, in this embodiment, the layer-2 unit 11 is arranged in the REC 7A. Accordingly, MAC-PDUs (i.e., a transport channel) are transferred from the REC 7A to the RE 7B.

In the example shown in FIGS. 12 and 13, the buffer 21 is arranged between the RLC unit 111 and the MAC unit 112. Accordingly, the buffer 21 shown in FIGS. 12 and 13 may store RLC PDUs (i.e., a logical channel) for each mobile station, for each bearer, for each QoS class, or for each mobile station and each QoS class. However, as described in detail in the first embodiment, the layout of the buffer 21 can be changed as needed. For example, the buffer 21 may be arranged between the PDCP unit 110 and the RLC unit 111.

Other Embodiments

The radio base stations 1 to 7 respectively described in the first to seventh embodiments may be relay stations. The relay station establishes a first radio link (a backhaul link) with a base station and establishes a second radio link (an access link) with a mobile station, thereby relaying data between the base station and the mobile station.

The bearer termination unit 10, the layer-2 unit 11, the BB-PHY unit 12, and the schedulers 20, 20A, and 20B, which are described in the first to seventh embodiments, may be implemented by using a semiconductor processing device including, for example, an ASIC (Application Specific Integrated Circuit) and a DSP (Digital Signal Processor). These units may be implemented by causing a computer, such as a microprocessor, to execute a program.

This program can be stored and provided to a computer using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as floppy disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g., magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R/W, and semiconductor memories (such as mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (Random Access Memory), etc.). The program may be provided to a computer using any type of transitory computer readable media. Examples of transitory computer readable media include electric signals, optical signals, and electromagnetic waves. Transitory computer readable media can provide the program to a computer via a wired communication line, such as electric wires and optical fibers, or a radio communication line.

The first to seventh embodiments can be combined as appropriate. Furthermore, the present invention is not limited to the embodiments described above, and can be modified in various manners without departing from the gist of the invention described above.

This application is based upon and claims the benefit of priority from Japanese patent application No. 2011-257479, filed on Nov. 25, 2011, the disclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   1-7 RADIO BASE STATIONS -   1A-7A RADIO EQUIPMENT CONTROLLERS (REC) -   1B-7B RADIO EQUIPMENT (RE) -   10, 10A, 10B BEARER TERMINATION UNITS -   11 LAYER-2 UNIT -   12 BB-PHY UNIT -   13 RF-PHY UNIT -   14 ANTENNA -   20 SCHEDULER -   20A PRIMARY SCHEDULER -   20B SECONDARY SCHEDULER -   21 BUFFER -   30, 31 INTERNAL INTERFACES -   40 TRANSMISSION LINE -   50 HANDOVER CONTROL UNIT -   110 PDCP UNIT -   111 RLC UNIT -   112 MAC UNIT -   120 CODING UNIT -   121 MODULATION UNIT -   122 RESOURCE MAPPING UNIT -   123 IFFT UNIT -   130 UP-CONVERTER -   131 AMPLIFIER 

1-38. (canceled)
 39. A radio station that is capable of transmitting and receiving user data including one of downlink user data and uplink user data to and from one or more mobile stations via an air interface, the radio station comprising: a central unit; and at least one distributed unit that can be arranged so as to be physically separated from the central unit, and is connected to the central unit via a transmission line so as to be able to communicate with the central unit, wherein the central unit comprises a first Layer-2 unit which is configured to control re-transmission for the downlink user data, and the distributed unit comprises a second Layer-2 unit which is configured to perform segmentation and concatenation for the downlink user data.
 40. The radio station according to claim 39, wherein the central unit is further configured to receive a request of the re-transmission for the downlink user data from the one or more mobile stations via the transmission line connected to the distributed unit.
 41. The radio station according to claim 40, wherein the re-transmission for the downlink user data is performed as processing of a Radio Link Control (RLC) layer, and the segmentation and concatenation for the downlink user data are performed as processing of the RLC layer.
 42. The radio station according to claim 41, wherein the central unit is further configured to perform processing of a Packet Data Convergence Protocol (PDCP) layer, and the distributed unit is further configured to perform processing of a Media Access Control (MAC) layer and a Physical layer.
 43. The radio station according to claim 42, wherein the central unit is further configured to connect with a core network via one or more network bearers. 